Touch screens are input devices that are useful in a variety of computer-based products, including cell phones, personal data assistants (PDAs), electronic books, point of sale terminals, and the like. Touch screens are usually formed with thin, transparent films that overlay a display so that the user can interact intuitively with objects and scenes on the display.
There are several known types of touch screens, including resistive, capacitive, infra-red, and acoustic. Capacitive touch screens have become the most popular due to their low cost, relative accuracy, and ability to detect multiple touches. Capacitive touch screens work by detecting small changes in capacitance due to the user's finger touching or being in close proximity to the screen. However because they rely on small changes in capacitance, capacitive touch screens are sensitive to false touch detections cause by, e.g., dust, water, etc. as well as to electromagnetic interference (EMI). Moreover it is difficult to discriminate between actual touches and objects such as fingers being in close proximity to the screen. In addition, capacitive touch screens cannot readily be scaled up in size because the signal discrimination becomes too low.
The use of the same reference symbols in different drawings indicates similar or identical items. Unless otherwise noted, the word “coupled” and its associated verb forms include both direct connection and indirect electrical connection by means known in the art, and unless otherwise noted any description of direct connection implies alternate embodiments using suitable forms of indirect electrical connection as well.